Nowadays, the liquid crystal displays (LCD) are generally used in all kind of information displays. The main structure of the LCD can comprise a panel module and a back light module. The panel module roughly comprises an Indium Tin Oxide (ITO) conductive glass substrate, a liquid crystal layer, an alignment film, color filters, polarizing sheets and a driver integrated circuit. The back light module mainly comprises a light source, a light guide plate, a prism sheet, a reflection sheet, a diffusion sheet and various optical sheets. The back light module is to provide the light source to the LCD. Generally, the performance of the LCD reflects the quality of every individual element. For example, the back light module plays an important role in the screen's brightness, intensity, contrast and visual angle.
The back light module can be generally classified into an extremity type and a bottom type, based on the light source. The light source of the extremity type is located at the side face of the back light module and thereby the thickness of the back light module can be reduced. In the market now, most light sources of the LCDs belong to this type of back light module. On the other hand, the light source of the bottom type is located under the back light module and thus better even brightness can be obtained. For the bottom type can provide a larger mounting space, it can contain more light sources and is suitful to be applied to the display requiring higher brightness and wider visual angle.
Due to rapid advance in the electronic manufacture technology, a recent breakthrough in the light effect of the LED can greatly help to improve the display ability of the LCD screens. Technically speaking, it is hoped that, by the year 2005, the light effect of the LED can exceed that of the cold cathode tube. Due to its swift response and feature in emitting visible light such as red, blue and green, the LED has a great opportunity to play a leading role in the light source of the LCD industry.
Referring to FIGS. 1A and 1B, FIG. 1A is an exploded view of a bottom lighting module with a conventional LED, and FIG. 1B is an cross-sectional view of the bottom lighting module of FIG. 1A in an assembled state. The back light module 1 comprises a PCB 10, a plurality of light-emitting diodes (LEDs) 14 and a heat sink 16. The PCB 10 has a first face 101, a second face 102 opposing to the first face 101, and a hole 103 connecting spatially the first face 101 and the second face 102.
The LED 14 disposed in the hole 103 comprises a light-emitting portion 141 and an LED-base 142. The LED-base 142 is inserted into the respective hole 103 to leave the light-emitting portion 141 above the PCB 10. The LED-base 142 comprises at least two electrodes 143 connected to the second face 102 of the PCB 10. For the two electrodes 143 electrically connects with the PCB 10, the PCB 10 can control to the LED 14.
The heat sink 16 comprises a main body 161 and a plurality of fins 162. One side of the main body 161 is set under the second face 102 of the PCB 10, while another face is used to form the fins 162. The heat sink 16 is usually made of a heat conduction material like aluminum or copper. Further, a heat sink medium 17 is accommodated in the sealed space formed between the heat sink 16 and the second face 102 of the PCB 10. The heat medium 17 is used to transport the heat generated by the LED-base 142 to the heat sink 16.
As illustrated in FIG. 1B, the back light module 1 uses a screw 19 to fasten firmly the PCB 10 and the heat sink 16. The PCB 10 has at least one aperture 122 for the screw 19 to penetrate downward through the PCB 10.
As illustrated in FIG. 2, a top view of FIG. 1B with the heat sink 16 locking firmly to the PCB 10 by the screw 19 is shown. The first face 101 of the PCB 10 has a plurality of holes 103 for inserting the respective LEDs 14.
As described above in FIG. 2, the PCB 10 needs to form a plurality of holes 103 in advance so that a corresponding number of the LEDs 14 can be inserted into the holes 103 one by one. In this process, using a mill machine to fabricate the holes 103 is usually expensive. Therefore, how to lessen above cost problem is deserved to discuss.
In addition, the connection way by screwing causes another drawback that affects light efficiency of the back light module. In the back light module 1, the first face 101 of the PCB 10 is usually adhered by a reflection sheet 18 and located under a diffusion sheet 15 that spaces from the reflection sheet 18 by a predetermined spacing. The light of the LED 14 would have a mixing effect in the sealed space formed between the reflection sheet 18 and the diffusion sheet 15
Hence, when the screw 19 integrates firmly the PCB 10 and the reflection sheet 18, the LED 14 emits the light to the diffusion sheet 15 and the LED light will reflect between the reflection sheet 18 and the diffusion sheet 15. However, the slit area around the screw 19 makes the reflection sheet 18 area piece-wise and would make the reflective LED light uneven. Definitely, the brightness and color of the light of the back light module 1 in accordance with the present invention would be greatly affected.